When manufacturing certain types of data storage discs, such as so-called DVDs, with one or more information layers, two substrate discs of polycarbonate of a thickness of 0.6 mm are normally glued together, with the information layer(s) adjacent to the adhesive layer joining the discs.
In one proposed method of glueing the adhesive is applied to one of the discs by means of a printing process, for example screen printing, whereafter the discs are joined together. This method does not waste adhesive and the application can be done very rapidly. However, there is some risk of air enclosures when the discs are put together and some risk that the printing system will break down should the screen printing blanket rupture.
A method using double adhesive tape for joining the two disc elements has also been suggested, but this method causes air enclosures and provides a joint of unreliable strength and thermal stability. Nor can this method be used for DVDs of the type "SD9", i.e. where both of the discs elements have information layers and where these layers are to be read by laser light which must pass, with the correct defraction, through the joint layer between the disc elements.